Sencha spotlight: The health benefits of Japanese tea
Catechins are a type of tannin and flavonoid unique to Japanese green tea.
Flavonoids are a sub-category of polyphenols (a type of micronutrient) that occurs naturally in plants. This component has been studied and is proven to assist with improving heart health, as well as raising immunity, among others.
Catechins are also the component responsible for the taste of astringency, or bitterness, in tea.
The four major catechins found in Japanese green tea are epicatechin (EC), epigallocatechin (EGC), epicatechingallate (ECG), and epigallocatechin gallate (EGCG).
As Japanese green tea, both sencha and matcha, are unoxidised after harvest, the level of the catechins found in the tea are different when compared to oxidised tea. This is further compounded by the steaming process, which allows the leaves to retain their natural colour, as well as their catechin levels.
Catechins are also studied to possess antioxidant properties several times higher than that of vitamin C and vitamin E.
As catechin dissolves at a higher temperature, this is part of the reason sencha may taste more bitter when brewed for the third time during a tea tasting event.
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In addition to improving heart health and containing high levels of antioxidants, catechins have also been studied to:
- Prevent the onset of hypertension.
- Suppress the levels of cholesterol.
Preventing the onset of hypertension
Hypertension or high blood pressure is considered a risk factor for lifestyle-related diseases such as heart attacks. While there are many various causes for hypertension including lifestyle habits, one key factor is a substance known as angiotensinogen.
Angiotensinogen is responsible for constriction blood in the vessels when it is converted from angiotension I to angiotensionn II. The catechins found in Japanese green tea however, have been shown to be able to suppress this conversion.
In a survey of 40,000 participants, the stroke mortality rate for frequent green tea drinkers was reportedly 35% lower for men and 42% lower for women. This data was made in comparison with participants who did not consume any green tea. (Shinichi Kuriyama et al., JAMA, 2006)
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In addition to improving heart health and containing high levels of antioxidants, catechins have also been studied to:
- Prevent the onset of hypertension
- Suppress the levels of cholesterol.
Suppressing the levels of cholesterol
The cholesterol levels present in bloodstream plays a role in inducing lifestyle-related diseases. Cholesterol is divided into two primary types: HDL cholesterol and LDL cholesterol.
When there is a high concentration of LDL cholesterol in the bloodstream, the cholesterol will collect in the walls of the blood vessel. This prevents blood from circulating smoothly. This is likely to lead to the development of medical conditions such as a heart attack.
Epigallocatechin gallate (EGCG), a type of catechin found abundantly in tea, has been studied to be effective in limiting LDL oxidation.
In a study, blood samples were taken from adults who consumed seven cups of tea daily (approximately 600g). Over a course of a week, test results showed that the LDL oxidation levels of these participants were significantly lower than the average adult. Furthermore, the HDL cholesterol levels in participants who consumed 400mg of catechin (approximately 6 cups of tea) daily over the course of three months, had increased. (Isao Tomita et al., 1998).
The catechins found in Japanese green tea have been studied to be capable of inhibiting the actions of α-amylase and sucrase. Inhibiting these two digestive enzymes suppresses the decomposition of starch and thus prevents the production of glucose.
By reducing the amount of fat produced from glucose, this is believed to indirectly prevent the drinker from gaining excess weight and reduce the risk of obesity.
In an experiment conducted on obese men, a research report found that participants who drank approximately 482mg of catechin daily had significantly less abdominal fat as compared to those who consumed only 180mg of catechin (Masa Hase, Ichiro Tokiko et al., 2001).
This benefit of catechin is believed to be compounded by the added interaction with caffeine, which is also present in tea.
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The rich umami flavour found in high-grade sencha, gyokuro, and matcha can be credited to the high levels of theanine found in the tea leaves. In fact, the majority of the amino acids found in Japanese green tea are theanine.
Aside from adding to the flavour profile, theanine is known to be good for improving mental impairment, as well as possessing relaxing qualities. The consumption of theanine produces α-brain waves, which reduces stress levels and allows the drinker to tap into a calmer state. Due to this effect, tea is also sometimes used as to aid in restful sleep.
Moreover, when combined with caffeine, the effects of both the amino acid (theanine) and stimulant (caffeine) are released slowly. The consumption of tea allows the drinker to indulge in these properties at a gentler pace.
